<template>
  <div class="spec-preview">
    <img :src="images.imgUrl" />
    <div class="event"  @mousemove="changeMove"></div>
    <div class="big">
      <img :src="images.imgUrl" ref="big" />
    </div>
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
  export default {
    name: "Zoom",
    props:['imageList'],
    data() {
      return {
        // 这里是定义大图的初始索引值  是响应式数据
        currentIndex:0
      }
    },
    computed: {
      images(){
        return this.imageList[this.currentIndex]||{};
      }
    },
    methods:{
         //鼠标移动事件
        changeMove(event) {
        //获取遮罩层
        let mask = this.$refs.mask;
        let big = this.$refs.big;
        //计算出移动的时候遮罩层l、t
        let l = event.offsetX - mask.offsetWidth / 2;
        let t = event.offsetY - mask.offsetHeight / 2;
        //约束left|top数值
        if (l <= 0) l = 0;
        if (l >= mask.offsetWidth) l = mask.offsetWidth;
        if (t <= 0) t = 0;
        if (t >= mask.offsetHeight) t = mask.offsetHeight;
        //动态修改遮罩层的l、t
        mask.style.left = l + "px";
        mask.style.top = t + "px";
        //修改大图的left|top
        big.style.left = -2 * l + "px";
        big.style.top = -2 * t + "px";
      },
    },
    mounted() {
      // 接收兄弟组件传递快来的索引值
      this.$eventBus.$on('send',(index)=>{
        // 下面这种写法:
        // 相当于给组件实例添加很随性  并非响应式数据
        // 响应式数据 --- 数据发生变化  视图立马变化

        this.currentIndex = index;
      })
    },
  }
  
</script>

<style lang="less">
  .spec-preview {
    position: relative;
    width: 400px;
    height: 400px;
    border: 1px solid #ccc;

    img {
      width: 100%;
      height: 100%;
    }

    .event {
      width: 100%;
      height: 100%;
      position: absolute;
      top: 0;
      left: 0;
      z-index: 998;
    }

    .mask {
      width: 50%;
      height: 50%;
      background-color: rgba(0, 255, 0, 0.3);
      position: absolute;
      left: 0;
      top: 0;
      display: none;
    }

    .big {
      width: 100%;
      height: 100%;
      position: absolute;
      top: -1px;
      left: 100%;
      border: 1px solid #aaa;
      overflow: hidden;
      z-index: 998;
      display: none;
      background: white;

      img {
        width: 200%;
        max-width: 200%;
        height: 200%;
        position: absolute;
        left: 0;
        top: 0;
      }
    }

    .event:hover~.mask,
    .event:hover~.big {
      display: block;
    }
  }
</style>